Two molecular weight components of human lymphoblastoid interferon have been purified and 75% amino acid sequence data obtained. Complete amino acid analysis of the two components has been performed as well as the fractionation of both cyanogen bromide and tryptic fragments of the 18,500 dalton component. The effect of exopeptidases on interferon activity has been determined. Interferon fragments 1-22, 1-26, 121-166, 72-166, and 27-166 have synthesized by Merrifield solid phase techniques. Investigation of the biological and immunological properties of these fragments is under way.